Commonly assigned U.S. Pat. No. 5,170,640 discloses an oil separator with a valve between the vortex oil separator and the coalescer. The valve is spring biased closed. The opening bias is provided by the differential pressure between compressor suction and discharge pressure which acts across the valve. Accordingly, the discharge pressure must build up to open the valve thereby insuring that a sufficient pressure is available to provide lubrication of the compressor prior to supplying refrigerant to the system. There is, therefore, a range of operating conditions over which the valve is closed or in a partially open position throttling the flow and reducing system operating efficiency.